The present invention is directed to a powerized stapler device and more particularly to a stapler device wherein the driving force imparted to the head of the stapler may be varied within a wide range such that a greater driving force is applied when a multiplicity of sheets are to be stapled and conversely, a lower driving force is applied where the staple is to be clinched through a limited number of sheets.
1. Prior Art
Powerized stapling devices have been available for many years, representative examples being disclosed in U.S. Pat. Nos. 2,403,947; 2,877,461; 2,957,174; 2,975,424; 3,016,538; 3,022,512; 3,026,518; 3,101,478; 3,151,329; 3,251,524, assigned to the assignee hereof. The references noted disclose, in general, staplers integrated into a housing, carrying an electromagnetic mechanism such as a solenoid, the armature of the solenoid being disposed above the drive head of the stapler. Insertion of articles to be stapled activates a switch mechanism energizing the solenoid and causing the armature to drive the stapler through an operating cycle
A difficulty inhering in staplers of the type described resides in the fact that the stapling force imparted is identical for stapling jobs consisting of a multiplicity of sheets and also for jobs involving only a few sheets. Where the applied force is sufficient for joining multiple sheets and the same force is utilized in joining jobs comprised of only a few sheets, one or the other of the jobs will be defective. More particularly, if the force is insufficient to drive a staple through a multiple sheet job, an effective clinching will not result. Conversely, if a force sufficient for multiple sheet stapling is utilized in connection with a two or three sheet job, the stapler will act in the manner of a punch, the base of the overdriven staple penetrating one or more of the sheets whereby the upper most ones of the sheets are not effectively connected to the remainder of the sheets.
A further problem inhering in the application of overly great stapling forces when connecting a limited number of sheets, resides in the excessive impact leaving an imprint surrounding the area of staple application.
A still further drawback of known powerized staplers, particularly when used to fasten a limited number of sheets, resides in the staple being applied with a rolling or angular clinch. The rolling clinch results from the fact that the sheets are moving a finite distance after the sensor, which activates the stapler, is energized. As a result, the legs of the staple penetrate the sheets while the sheets are still moving, whereby the base of the staple has passed a slight distance beyond the clinching anvil, resulting in a rolling or loosely applied staple. The described problem is of lesser significance where a multiplicity of sheets are to be stapled since the multiple sheets act as a support for the staple as it is driven. Additionally, the thickness of the multiple sheets assures that impact between the stapler head and the upper most sheet occurs promptly following energizing of the power mechanism since the upper most sheet of a thick stack will be closer to the stapler head than would be the case where only a few sheets are to be connected.
Various means have been proposed to provide stapling devices wherein the driving power may be adjusted. These known devices utilize electronic circuitry for varying the voltage applied to the solenoid or other electromagnetic driving means. While these devices enable the user to tailor the driving force, within a limited range, to the job at hand, they do not solve the problems discussed above, and particularly the problem of avoiding a rolling staple connection when used to join a limited number of sheets.
A further drawback of known powerized staplers resides in the fact that the power must be manually adjusted in accordance with the job at hand. Thus, where the user will sequentially staple thin and thick stacks of articles, adjustment must be manually effected between each application, greatly slowing the stapling procedure. Additionally, manual adjustment involves discretion on the part of the user and thus is a minimal aid to the occasional powerized stapler user.